This invention concerns an impeller for centrifugal pumps meant for pumping liquids.
More precisely, the invention concerns an impeller of the so-called single vane type, which means that the impeller is provided with one single vane extending helically or along a screwline around the impeller a part of, one or several turns. The channel formed by the vane is axially limited by cover discs, which are parts of the impeller or the surrounding pump housing.
Pump impellers of the type referred to above are all used for pumping liquids containing solid bodies, for instance, sewage water. The advantage is that the risk for clogging decreases if one instead of several vanes are used. Sometimes a certain minimum throughlet in a pump impeller for sewage pumps is prescribed by law. This can only be fulfilled by single vane impellers if reasonable dimensions should be kept.
In order to further diminish the risks for clogging, it is sometimes preferable to design the vane with a varying thickness so that the channel formed by the vane and the cover discs has a relatively constant cross-section in the direction towards the outlet. (Swedish Patent Application No. 7903729-7)
A problem which occurs by these impellers is that they become unbalanced under certain conditions which causes vibrations in the pump unit. This may be eliminated by balancing weights in the impeller which means that the problem is solved when the pump operates under normal conditions, that is, submersed in liquid. If, however, the pump operates in air, the problem with vibrations remains and as those pumps sometimes operate during such varying conditions, the solution with balancing weights is not entirely satisfactory. Another problem which often occurs by single vanes is an extensive efficiency loss.